Veli Vikberg

LARVAL HABITS, HOST-PLANT ASSOCIATIONS, AND SPECIATION IN NEMATINE SAWFLIES (HYMENOPTERA: TENTHREDINIDAE)

Abstract Adaptive radiations consist of two intertwined processes, diversification of species and diversification of their ecological niches, but it is unclear whether there is a causal link between the processes. In phytophagous insects, ecological diversification mainly involves shifts in host-plant associations and in larval feeding habits (internal or external) on different plant parts, and several observations indicate that speciation is facilitated by host shifts. Data on host use in individual species suggest that internal feeders are less likely to colonize new hosts than external-feeding taxa and, consequently, increases in collective host ranges and species numbers should be slowed down in endophagous lineages. We tested these related hypotheses by using phylogenetic information to reconstruct the evolutionary history of larval resource use in the sawfly subfamily Nematinae, a group of 1000 plus species with a broad range of niches: the subfamilys combined host range includes over 20 plant families, and larvae may feed externally on leaves or needles, or internally, for example, in buds, fruits, leaves, or galls. The results show that: (1) Most internally feeding groups have evolved independently from external-feeding ancestors, but several distinct internal habits have appeared convergently multiple times; (2) Shifts among host taxa are clearly more common than changes in larval habits; (3) The majority of host switches have occurred among phylogenetically close plant groups, but many shifts are manifest among distantly related, ecologically proximate hosts; (4) Although external feeding characteristic of the common ancestor of Nematinae is associated with relatively high rates of host-shifting, internal feeders are very conservative in their host use; (5) In contrast, the effect of endophagy on speciation probabilities is more variable: net speciation rates are lowered in most internal-feeding groups, but a striking exception is found in species that induce galls on Salicaceae. The loose connection between collective host ranges and species diversity provides empirical support for theoretical models suggesting that speciation rates are a function of a complex interplay between “intrinsic” niche width and resource heterogeneity.

Molecular phylogeny of the sawfly subfamily Nematinae (Hymenoptera: Tenthredinidae)

Abstract Nematinae is one of the largest subfamilies in the sawfly family Tenthredinidae, but internal relationships are unknown in the absence of any formal phylogenetic analysis. To understand the internal phylogeny of Nematinae, we sequenced a portion of the mitochondrial cytochrome oxidase I gene and the nuclear elongation factor‐1α gene from thirteen outgroup taxa and sixty‐eight nematine species, the ingroup taxa of which represent all major genera and subgenera within the subfamily. Maximum parsimony and Bayesian phylogenetic analyses of the DNA sequence data show that: (1) Nematinae are monophyletic in a broad sense which includes Hoplocampa, Susana and the tribe Cladiini, which have been classified often into separate subfamilies; together with Craterocercus, these taxa form a paraphyletic basal grade with respect to the remaining Nematinae, but among‐group relationships within the grade remain weakly resolved; (2) the remainder of the ingroup, Nematinae s. str, is monophyletic in all combined‐data analyses; (3) within Nematinae s. str, the ‘Higher’ Nematinae is divided into three groups, Mesoneura and the large tribes Nematini and Pristiphorini; (4) although the traditional classifications at the tribal level are largely upheld, some of the largest tribes and genera are obviously para‐ or polyphyletic; (5) according to rate‐smoothed phylogenies dated with two fossil calibration points, Nematinae originated 50–120 million years ago. In addition, the results from all Bayesian analyses provide strong and consistent support for the monophyly of Tenthredinidae, which has been difficult to demonstrate in previous parsimony analyses of morphological and molecular data.

Community structure, survival and mortality factors in arctic populations of Eupontania leaf gallers

Abstract. We studied survival, mortality factors, and community structure of nine species of leaf-galling sawflies, Eupontania spp., living on ten willow species (Salix spp.) at six sites on the Russian arctic tundra. The sawfly species represented two different gall types: the viminalis-type, which forms pea-shaped galls on the underside of leaf blades, and the vesicator-type, which forms bean-shaped galls on both sides of the leaf blade. Gall communities in the northernmost site had only one parasitoid species, but up to six parasitoids were found at the southernmost site. Inquiline parasitoids were encountered only in the two southern sites. Survival of the larvae varied between 20.0 and 82.8% among galler species at different sites. Parasitoids were the most important mortality factor for the sawflies. They caused mortality of 7.8–65.4%, depending on galler species and site, and it was highest in the northernmost site. Plant-specific mortality varied from 1.7 to 28.4% by galler species and it tended to decrease towards the north. Mortality from parasitoids was greater in the vesicator-type gallers than in the viminalis-type gallers. The total mortality caused by parasitoids in the arctic communities does not appear to differ from that in the diverse southern communities of Eupontania in Middle Europe, Scandinavia and North America, despite the assemblage having only a few members in the Arctic. The largest difference between the southern and the northern communities was the lack of inquiline parasitoids in the north. Our data do not support the hypothesis that abiotic, rather than biotic, factors would be more important in determining the abundance of populations of herbivorous insects in the harsh arctic environment.

Determinants of parasitoid communities of willow-galling sawflies: habitat overrides physiology, host plant and space.

Studies on the determinants of plant–herbivore and herbivore–parasitoid associations provide important insights into the origin and maintenance of global and local species richness. If parasitoids are specialists on herbivore niches rather than on herbivore taxa, then alternating escape of herbivores into novel niches and delayed resource tracking by parasitoids could fuel diversification at both trophic levels. We used DNA barcoding to identify parasitoids that attack larvae of seven Pontania sawfly species that induce leaf galls on eight willow species growing in subarctic and arctic–alpine habitats in three geographic locations in northern Fennoscandia, and then applied distance‐ and model‐based multivariate analyses and phylogenetic regression methods to evaluate the hierarchical importance of location, phylogeny and different galler niche dimensions on parasitoid host use. We found statistically significant variation in parasitoid communities across geographic locations and willow host species, but the differences were mainly quantitative due to extensive sharing of enemies among gallers within habitat types. By contrast, the divide between habitats defined two qualitatively different network compartments, because many common parasitoids exhibited strong habitat preference. Galler and parasitoid phylogenies did not explain associations, because distantly related arctic–alpine gallers were attacked by a species‐poor enemy community dominated by two parasitoid species that most likely have independently tracked the gallers’ evolutionary shifts into the novel habitat. Our results indicate that barcode‐ and phylogeny‐based analyses of food webs that span forested vs. tundra or grassland environments could improve our understanding of vertical diversification effects in complex plant–herbivore–parasitoid networks.

Latitudinal and Altitudinal Patterns in Species Richness and Mortality Factors of the Galling Sawflies on Salix Species in Japan

Species richness of willow species and galling sawflies living on them were examined in latitudinal and altitudinal gradients in six Japanese river systems from Hokkaido to southern Honshu. Mortality factors of gallers including plant based mortality, parasitoids and inquilines during larval development were studied by dissecting sampled galls under a microscope. The association between environmental factors, mortality factors and local diversity of galling sawflies and their willow hosts were studied. Species richness of sawfly gallers and their host plants decreased towards the south. Species richness of gallers was lower in the delta areas at lower altitudes than at higher altitudes. Different mortality factors, plant based mortality, parasitoids or inquilines, showed no significant trends with latitude or altitude. Although some parasitoids showed a weak correlation with latitude and altitude, but overall survival of larvae was not correlated with latitude or altitude. Among sawfly gall types, Pontania proxima-type was distinct by having high plant-based mortality. The observed pattern of increasing diversity with increasing latitude is opposite to that in many other animals and plants. This pattern is unlikely explained by larval survival or different mortality factors since they showed no difference in latitudinal or altitudinal gradient. A possible explanation of the pattern may be the decreasing host plant richness with other host related factors, like increased habitat fragmentation and decreased abundance of host plants towards the south. In addition, leaf flush of host plants and egg laying of galling sawflies might be better synchronised in north with highly seasonal but predictable resource availability.

Corrigenda: North-Western Palaearctic species of Pristiphora (Hymenoptera, Tenthredinidae). Journal of Hymenoptera Research 59: 1–190. https://doi.org/10.3897/jhr.59.12656

It has come to our attention that we used the term “scopa” incorrectly throughout our revision of north-west Palaearctic Pristiphora species (Prous et al. 2017, p. 12 et seq.), and in the associated electronic identification key available at figshare (http://dx.doi. org/10.6084/m9.figshare.5235805). The term is in frequent use for assemblages of stiff hairs, on the legs or abdominal sterna, used for transporting pollen in bees (Huber and Sharkey 1993). Our intention, in sawflies, was to denote an invagination or concavity at the tip of the sawsheath (e.g. Figs 75, 104–107, 111, 115, 121 in Prous et al. 2017) that distinguishes such sawsheaths from unmodified ones (e.g. Figs 98–99 in Prous et al. 2017), or from those having a “carina” (e.g. Figs 66–69 in Prous et al. 2017). The meaning of “scopa” (from Latin “broom”) in the context of Symphyta, consistent with most recent literature, is a paired, latero-posteriorly projecting structure at the tip of the sawsheath (Ross 1937: 76, Smith 1988: 229, 1992: 4). The “scopa” of sawflies sometimes bears a clearly defined setose area, often conspicuous in Diprionidae, termed “scopal pad” by Ross (1955) and Smith (1988). A potential source of further confusion is the use by some authors of “scopa” for the scopal pad alone (e.g. Hara and Shinohara 2015). In future, it might be preferable to restrict the use of the word scopa to the JHR 63: 125–126 (2018)